Lubricating oil compositions for gasoline fueled engines and diesel engines typically contain a variety of additives such as detergents and dispersants, antiwear agents, etc. Lubricating oils for medium- or low-speed diesel engines are known and will typically contain a range of additives which will perform a variety of functions: for example they may comprise dispersants to minimize deposit formation in various parts of the engine or detergent additives. However contamination of these lubricating oil compositions with unburned residual fuel oil is a problem recognized in the industry. This leads to severe engine cleanliness problems in service, which is sometimes referred to as “black paint.” The problem is particularly widespread in 4-stroke trunk-piston engines where dirty cam boxes and crankcases are encountered. However, the problem is not confined to 4-stroke engines; 2-stroke crosshead engines can also suffer from the problem. These 2-stroke engines will usually use two separate lubricating oils, one for the crankcase and one for the cylinder, but it is in the crankcase where the heavy deposits potentially occur. It might be expected that the problem would be overcome simply by using more of the conventional dispersant additive in the lubricating oil, but this measure has met with very limited success.
Acidity in lubricating oil is another long-recognised problem. In the operation of the internal combustion engine by-products from the combustion chamber often blow by the piston and admix with the lubricating oil. Additives are generally employed to neutralise the acidic materials and disperse sludge within the lubricating oil. Examples are overbased alkaline earth metal sulfurized hydrocarbyl-substituted phenates, salicylates, naphthenates and sulfonates. The term “overbased” is generally used to describe those alkaline earth metal hydrocarbyl-substituted salts in which the ratio of the number of equivalents of the alkaline earth metal moiety to the number of equivalents of the acid moiety is greater than one. The ratio is usually greater than 1.2 and may be as high as 4.5 or greater. In contrast, the equivalent ratio of alkaline earth metal moiety to acid moiety in “normal” or “neutral” alkaline earth metal hydrocarbyl-substituted salts is one, and in “low-based” salts is less than one. The metal ratio is referred to herein by the term “MR.” The overbased material usually contains greater than 20% in excess of the alkaline earth metal present in the corresponding neutral material. For this reason overbased alkaline earth metal hydrocarbyl-substituted salts have a greater capability for neutralising acidic matter than do the corresponding neutral alkaline earth metal hydrocarbyl-substituted salts, though not necessarily an increased detergency power. The degree of overbasing is expressed as “Total Base Number” or TBN, which is also sometimes referred to as Alkalinity Value or AV, and is measured by the method of ASTM Procedure D-2896.
International publications WO 99/25677 and WO 99/25793 disclose calixarenes containing within the calixarene ring at least one salicylic acid. The use of these compounds as fuel additives and lubricant additives is disclosed. Metal salts of these compounds as well as the use of such metal salts as lubricant additives are disclosed. These references indicate that in order to provide the calixarene ring structure it is necessary to use a reaction mixture containing at least 50% by weight solvent, preferably at least 80% by weight solvent, more preferably at least 90% by weight solvent. The references indicate that at solvent concentrations well below 50% by weight linear molecules are formed.
Copending U.S. patent application Ser. No. 09/802,500 filed Mar. 9, 2001, relates to linear phenol-salicylic acid condensation products used as lubricant and fuel additives.
European Patent Publication EP 0708171 A2 relates to lubricants containing metal salts, preferably overbased salts, of hydrocarbyl-substituted carboxyalkylene-linked phenols, dihydrocarbyl esters of alkylene dicarboxylic acids, the alkylene group being substituted with a hydroxy group and an additional carboxylic acid group, or alkylene-linked polyaromatic molecules, the aromatic moieties whereof comprise at least one hydrocarbyl-substituted phenol and at least one carboxy phenol, where the hydrocarbyl groups are of sufficient length to provide oil solubility to the salts and the salts exhibit good asphaltene suspension for marine diesel applications.
One object of this invention is to provide dispersant and detergent compositions for use in lubricating oil compositions.
Another object is to provide lubricating oil compositions with improved dispersancy performance, particularly with respect to reduction or elimination of “black paint” deposits.
It has now been found that considerably improved performance with respect to reduction or elimination of ‘black paint’ can be obtained with the compositions of this invention wherein the phenolic segments are substituted with hydrocarbyl groups containing on average at least 18 carbon atoms. It has also been observed that these provide excellent antioxidant properties. Moreover, we have also found that this effect is so marked that the phenolic sections may not have to be purely C18 or greater substituted hydrocarbyl phenols, they can be mixtures of lower than C18 and greater than C18 substituted hydrocarbyl phenols with no loss in anti-black paint performance, and possible economic advantages.
One of the main contributors to the sulfur and phosphorus level in a crankcase engine oil is the zinc dithiophosphate (ZDTP) antiwear agent. When the novel C18−18+ alkylphenol-formaldehyde-salicylic acid resin compounds of this invention are overbased in the presence of boric acid so as to contain boron in the end overbased product, these are both good antiwear agents and detergents which can partially or fully replace ZDTP antiwear agents and sulfur-containing overbased detergents. The ZDTP antiwear agent level in the crankcase engine oil may be reduced, thus lowering the phosphorus and sulfur content of the crankcase engine oil. The sulfur level will be reduced further by the presence of sulfur free novel boron containing compound rather than traditional sulfur containing overbased detergents such as phenates and sulphonates.